The present invention relates to a novel electrode arrangement and method for effecting cardioversion with an automatic implantable device. The electrode arrangement includes a catheter electrode intravenously positioned within the heart of a patient wherein one electrode on the catheter is within the left ventricle and a second electrode on the catheter is within the superior vena cava or in the right atrium. A third electrode, in the form of a flexible, substantially planar patch, is subcutaneously positioned outside the thoracic cavity in the region of the left ventricle. The two electrodes on the catheter are electrically connected together during a discharge, and are placed at a polarity opposite from that of the patch electrode.
Approximately 250,000 Americans under the age of 65 die annually from a condition termed "sudden cardiac death". In the vast majority of these cases, the cause of death is ventricular tachycardia and/or ventricular fibrillation. An automatic implantable cardioverting/defibrillating device has been developed and shown to be effective in preventing sudden cardiac death from these causes. See, for example, U.S. Pat. No. 4,407,288.
As used herein, the term cardioversion generally may be defined as the correction of either ventricular tachycardia or ventricular fibrillation by the discharge of electrical energy into the heart (0.1-40 joules when discharged through internal electrodes). Ventricular tachycardia is an abnormally rapid heart rate (120-180 beats per minute) originating in the heart's main pumping chambers (ventricles) which is regular in periodicity and oftentimes is life threatening to the patient. Ventricular fibrillation is generally a more rapid heartbeat disorder, disorganized and irregular, or non-periodic, and is fatal unless corrected within minutes by the discharge of electrical energy through the heart. More specific medical terminology often uses the term cardioversion to mean the synchronized delivery of an electrical shock to the heart to correct ventricular tachycardia. Defibrillation, then, is often referred to as the nonsynchronized delivery of electrical energy to the heart to correct ventricular fibrillation. Internal cardioversion is usually effective with. 0.1 to 3 joules of electrical energy when delivered in synchronism with the electrical heartbeat. Internal defibrillation requires 5 to 30 or more joules of electrical energy, depending largely on the electrode system used.
Over the years, many different types of electrode systems have been suggested for use with the automatic implantable cardioverter/defibrillator. For example, U.S. reissue Pat. No. Re. 27,757 describes an electrode arrangement whereby one electrode is formed on the distal end of an intravascular catheter that is positioned within the right ventricle, whereas the second electrode is positioned on the surface of the chest or sutured under the skin of the chest wall or directly to the ventricular myocardium.
U.S. Pat. No. 3,942,536 discloses a catheter electrode system wherein both electrodes are on a single intravascular catheter. The distal electrode is wedged in the apex of the right ventricle and the proximal electrode is immediately superior to the right atrium.
An improved intravascular catheter electrode system is described in U.S. Pat. No. 4,603,705. There, the proximal electrode is located in the superior vena cava and the distal electrode is in the right ventricle. A sensing and pacing electrode is also provided at the distal tip of the catheter. The first two electrodes constitute the anode and cathode of the cardioverting/defibrillating electrode pair; the tip electrode is used for sensing heart rate and pacing the heart. Using this single catheter system, energies required to defibrillate the human heart have been found to vary between 5-40 joules, but in some 40-50% of patients, even the higher energies may be insufficient to defibrillate the heart. Thus, although this improved catheter electrode system has many advantages, such as the capability of being installed without surgically invading the thoracic cavity, it has been found to have somewhat limited effectiveness in terminating ventricular anhythmias.
Various other electrode arrangements have also been employed. In U.S. Pat. No. 4,030,509, for example, the implantable electrode system includes, among others, a flexible apex electrode designed to surround the apex of the heart, and various flexible base electrodes designed to surround the base of the heart.
Another electrode arrangement and discharge method can be found in U.S. Pat. No. 4,548,203. There, three or more patch electrodes are connected and used in a discharge pattern involving the sequential delivery of multiple shocks across the heart, with such sequential shocks being in transverse directions to one another. The patentees explain that by issuing sequential shocks across opposed pairs of electrodes, a more uniform discharge pattern develops, resulting in more effective cardioversion and hence lower discharge energies.
Typical electrodes presently being used in conjunction with the commercially available automatic implantable cardioverter/defibrillator consist of one catheter defibrillating electrode adapted to be placed in the superior vena cava/right atrial region, and a second flexible, conformal, defibrillating patch electrode adapted to be placed on the outside of the heart, typically over the lateral wall of the left ventricle. See, U.S. Pat. Nos. 4,161,952 and 4,270,549. Placement of the first catheter-mounted electrode can be accomplished by insertion into one of the veins outside the thorax and sliding the catheter electrode into the venous system until the electrode portion is within the thorax and located at the junction of the superior vena cava and right atrium. Thus, for the placement of this electrode, it is not necessary to surgically enter the thorax. For the second electrode, however, it is necessary to make one of a variety of surgical incisions to open the thoracic cavity in order to place the electrode over the left ventricle of the heart. Each of these surgical approaches has disadvantages. Two such approaches involve major surgery and substantial patient recovery time with a cost currently between $8,000-12,000. These approaches consist of splitting the sternum (breastbone) or alternatively opening a space between the ribs in order to gain access to the surface of the heart. A third approach involves making a smaller incision under the xiphoid process, which is simpler from a surgical point of view, but still involves entering the thoracic cavity. Moreover, this approach sometimes does not allow convenient positioning of the left ventricular electrode. And in many instances, two patch electrodes are used, rather than one patch and one catheter electrode.
With this background, there was developed an electrode arrangement and discharge method which does not involve the surgical opening of the thoracic cavity. Specifically, in copending U.S. patent application Ser. No. 795,781, filed on Nov. 7, 1985 and assigned to the present assignee, incorporated herein by reference, there is disclosed an electrode system that includes an intravascular catheter insertable within the heart of a patient, and having a first electrode adjacent the distal end of the catheter and a second electrode positioned at the proximal end of the catheter; this catheter electrode can be of the type described in Pat. No. 4,603,705, incorporated herein by reference. Associated with this bipolar catheter electrode is a third electrode, in the form of a flexible patch electrode, that is placed subcutaneously outside the thoracic cavity, but proximate the apex of the left ventricle. The patch electrode is electrically connected with the second electrode of the catheter, the latter of which is positioned in the superior vena cava/right atrium region. The first, or distal, electrode of the catheter, completes the cardioverting/defibrillating circuit. A pulse of electrical energy is discharged between the first electrode and the combined second electrode/patch electrode.
It subsequently has been theorized that while the electrode placements and connections as described immediately above does, indeed, reduce the energy needed for effective cardioversion/defibrillation, it may be possible to still further reduce the necessary discharge energy. Specifically, by changing the polarity of discharge so that the discharge travels more effectively and uniformly across the myocardium, it may be possible to effect cardioversion at even lower energies with a single shock.